Boron is a commonly favored P-type dopant in the semiconductor manufacturing industry and is commonly used in CMOS, BiPolar and BiCMOS technologies. Silicon nitride, films are used extensively in semiconductor manufacturing for various functions, various applications, and in various technologies. When SiN films are formed, using the various methods of formation, hydrogen is invariably incorporated into the film. For example, silane (SiH4) is a source gas commonly used as the silicon source in the various processes used to form silicon nitride films. The hydrogen incorporated within the SiN film forms bonds with both the silicon (Si—H bonds) and the nitrogen (N—H bonds) components of the film. Si—H bonds include a higher activation energy than N—H bonds. As such, hydrogen that is bonded to nitrogen, as opposed to being bonded to silicon, is more susceptible to becoming dissociated from its bond and migrating throughout and from the SiN film. During various high-temperature processes, such un-bonded hydrogen urges boron diffusion when boron is used in the semiconductor device being formed. Such boron diffusion may result in boron penetration and boron-doped poly depletion. Because of the relative activation energies, it has been found that only the N—H bonded hydrogen contributes to the above-mentioned anomalies that negatively impact the device.
Processing operations carried out at elevated temperatures cause hydrogen to dissociate from N—H bonds. Boron is commonly used as the P-type dopant in polycrystalline silicon and other material. During high temperature operations, the presence of available, un-bonded hydrogen enhances the diffusion of boron from the P-doped polycrystalline silicon material. For example, in a CMOS transistor, in particular, a PMOS transistor, boron from the polycrystalline silicon, hereinafter “polysilicon”, gate, may diffuse from the gate and into the gate oxide and/or the transistor channel. Such diffusion, a.k.a. boron penetration, is aided by the availability of free hydrogen such as hydrogen that was bound to nitrogen. In conventional silicon nitride films, hydrogen bound to the nitrogen is much more prevalent than hydrogen bound to silicon due, in part, to the conventional SiN film being substantially nitrogen-rich. In MOSFET technology, when conventional silicon nitride spacers are formed adjacent the poly gate, the hydrogen, prevalently bonded with nitrogen of the silicon nitride film and forming a weak bond therewith, breaks free and enhances boron diffusion during subsequent high-temperature processing operations such as the source/drain anneals typically carried out at temperatures within the range of 1000-1100° C. Such boron penetration into the transistor gate oxide or the transistor channel, shifts the Vt (threshold voltage) of the transistor at the least, and may completely destroy transistor performance.
Another mechanism in which un-bonded hydrogen negatively impacts device performance is boron-doped poly depletion. Hydrogen that was formerly bound to nitrogen, becomes liberated and pairs with boron, an acceptor, to render the boron atom electrically inactive. According to this mechanism, the concentration of the P-type boron acceptor atoms is diminished in the polysilicon.
In the various technologies presently used in the semiconductor manufacturing industry, such as Embedded SRAMs, Enhanced SRAMs SiGe and other BiCMOS technologies, and advanced CMOS processes, silicon nitride material is commonly used for various applications such as spacers, salicide blocks and liners, and various insulators. Nitride films are also used as masking films to assist in the formation of other device features. Moreover, such technologies typically use boron-doped polysilicon materials for various structural and interconnect features. It would therefore be desirable to form silicon nitride materials in which the amount of hydrogen bound in Si—H bonds is increased, and the amount of hydrogen bound in N—H bonds, is decreased. It would likewise be desirable to form such a film using a low thermal budget. In this manner, the hydrogen remains bonded to the silicon nitride film and does not enhance the aforementioned mechanisms of boron penetration and boron-doped poly depletion that negatively impact semiconductor devices.